Study of the fast dynamics of optical aberrations on Nd:glass flash-pumped kilojoule-class laser chains toward the coherent beam combining

Increasing the repetition of kilojoule-class laser chains has recently strongly gained in interest, especially in the context of inertial confinement fusion (ICF). A promising approach is the coherent beam combination (CBC) of smaller-scaled laser sources of higher repetition rate, to overcome the critical cooling problems of single very large aperture amplifiers. This method has already proved its worth in low-energy systems and especially with very higher repetition rates [1] and has been widely applied in industrial settings using fiber systems [2]. However, since high-energy laser chains have diameters of several tens of centimeters, new challenges appear. First, the spatial issues must be taken into account, as phase correction limited to piston adjustment is insufficient. Second, due to the low repetition rate a feedback loop relying solely on laser shots is inadequate because it lacks information on phase variations occurring between shots. Many large laser facilities thus see coherent beam combining as an up-and-coming technique, but paradoxically, the literature lacks data on the wavefront evolution during the flash duration [3]. We therefore propose a study to characterize these phenomena aiming to conclude on the key issues and any potential no-go for combining coherently kilojoule-class lasers.